As though he had done it a hundred times before, Septimus opened the door to the moving chamber and touched the orange arrow. As the chamber began to move, Septimus allowed himself a smile at Beetle's dumbstruck expression. Neither said a word - Beetle was speechless, and Septimus was calculating whether they would have time to get back to the chamber before Tertius Fume and the jinn emerged from the stairs. It was going to be close. Nervously he fingered the Alchemie Keye, which he had taken off in readiness.

The arrow crept downward. Septimus spoke. "Beetle, are you sure you want to come the rest of the way? Because if you don't...well, you know I don't mind, I really don't. You can wait here. I can show you how to take this thing back up - just in case."

"Don't be silly, Sep."

The moving chamber suddenly slowed, and Beetle's stomach shot up to his ears.

"Hey, Sep - where have you gone?" he said.

The chamber settled to a halt.

"Can't you see me?" asked Septimus, concerned - his hand hovering by the door panel.

"Nope. You've disappeared."

"It's your UnSeen that's disappeared."

"Oh, gosh, I'm really sorry," said Beetle. "I dunno what happened."

Septimus let go of his UnSeen.

"Oh, there you are, Sep. That's better."

"We'll try them again - together, okay?" said Septimus. "One, two, three..."

"You've gone again!" said Beetle.

Septimus reappeared. "One more time - okay?"

"Yep. Here goes."

"You count this time, Beetle. Do it when you're ready. Sometimes that helps."

"Okey-dokey," said Beetle, sounding more confident than he felt. It didn't work.

Septimus was aware that time was ticking away. With every second the warrior jinn were getting closer - and every second passed was one less second they had to get back to the moving chamber. He made a decision. "We'll do without. Who needs UnSeens anyway?" He swiped the door open, and Beetle followed him into the wide, brick passageway with the hissing lamps. They raced through the cold air, clattered down the flight of steps and skidded to a halt in front of the shiny black dead-end wall. Septimus ran his hand across the worn patch on the wall, and the door slid open. They stepped inside the ice chamber. With a soft swish and a click the door closed and the blue light came on. Wide-eyed, Beetle stared at the massive Ice Tunnel hatch swimming with water, shining with ancient gold.

"That is some hatch," he gasped.

Septimus was already on his knees, looking for the Sealing Plate.

"Hey, look at all the scribing in the gold," said Beetle, completely forgetting about the oncoming jinn in his excitement. "This hatch is incredibly old. One day we're going to have to come back. I could bring some translations with me. Just think, if we could read what it says - "

Septimus placed the Keye into the Sealing Plate.

Suddenly the rhythmic thud of marching feet on stone came through the walls of the chamber - the jinn had reached the corridor. Beetle came back to reality. He and Septimus looked at each other, translucently pale, as though they were drowning in the thin blue light.

"I guess we're...trapped," whispered Beetle.

"Yeah," said Septimus, trying to keep his voice steady, while concentrating on holding the Keye still. A skin of ice began to snake out from the Keye and encircle the lozenge-shaped hatch. "But at least they can't get to the Castle now."

"The Castle...oh, my gosh - why didn't I think of it before?" said Beetle. "Sep, you got your whistle for the Wizard Tower sled?"

"Yes - why?" Septimus was watching the slow progress of the ice, willing it to move faster.

"Brilliant! Sep, stop right there. UnSeal it!"

"Beetle, are you crazy?"

"No. We'll get into the tunnel and Seal it from inside. Then you whistle for the Wizard Tower sled and we go home - simple!"

Septimus heard the marching footsteps coming nearer - and suddenly he realized something. Unless he did an UnSeen, Tertius Fume would simply get the jinn to take the Keye off him and UnSeal the hatch. Beetle clearly could not manage another UnSeen, so if Septimus did do one, Beetle would be with the jinn -  alone. It was a terrible thought.

"Okay!" Septimus slammed the Keye reverse-side down onto the Sealing Plate and the narrow band of ice melted.

Beetle pulled opened the ice hatch. Below him was the widest, deepest - and surely the darkest - Ice Tunnel he had ever seen. A blast of freezing air met him. The sound of footsteps rang on the steps outside.

"Halt!" Tertius Fume's bellow came through the door. "Open the door." A metallic clang sounded. Nothing happened. Septimus smiled - one of the drawbacks of having weapons for hands was that it was much harder to open palm-press doors. Beetle swung over the edge of the open hatch and lowered himself into the darkness, his feet searching for a foothold. He grinned. "Rungs," he said, and disappeared. Septimus followed fast. He found the rungs and tugged the ice hatch closed. Slowly, slowly - horribly slowly - the hatch moved down to its Seal. The door to the ice chamber swish ed open, and Septimus caught a brief glimpse of Tertius Fume's ghostly blue robes and knobby sandaled feet before the hatch settled onto its Seal. Inside the tunnel everything went black. For a moment Septimus could see nothing - where was the Sealing Plate? On the other side of the hatch, as Tertius Fume bellowed at the first two jinn to raise the hatch, Septimus's Dragon Ring began to glow, its yellow light reflecting off the gold Sealing Plate.

Septimus slammed the Keye onto the plate and, in the ice chamber, Tertius Fume stared in astonishment as a diamond-hard ring of Sealing ice encircled the hatch. His furious bellow penetrated the hatch.

"Glad we're down here," said Septimus.

"Yeah," said Beetle.

His hands already chilled, Septimus brought out a tiny silver whistle and blew hard. As always, no sound came out.

"Do you think it worked?" he said.

"Yeah," said Beetle. "Of course it did."

Beetle was right. Far away, in a lonely Ice Tunnel underneath Beetle's old hut in the backyard of the Manuscriptorium, the Wizard Tower sled Awoke to the happy sound of its Magykal whistle. It curled its carelessly flung purple rope into a neat coil, and in seconds its fine golden runners were cutting crisply along the frost, setting off for unknown territory and pristine ice.

Septimus and Beetle took stock. They could not see much by the light of the Dragon Ring, but what they could see was enough to tell them that this was no ordinary Ice Tunnel. It was, as Beetle put it, the Grandmother of all Ice Tunnels. It was also, he pointed out, wide enough for a ten-sled race and as high as the tallest Manuscriptorium bookshelf. And it was cold. Beetle shivered. The cold in the Ice Tunnel seemed much worse than he remembered.

From far above came Tertius Fume's angry shout - muffled but clear enough.

"Axmen, smash the hatch!"

There was a tremendous crash and a shower of ice rained down. Beetle leaped out of the way.

"They can't break it open, can they?" said Septimus, glancing up anxiously.

"Well...I dunno." Beetle looked worried. "I suppose if they go on long enough they might."

"But I thought ice hatches were indestructible," said Septimus.

"I d-don't think they've been tested against warrior j-jinn," said Beetle, his teeth beginning to chatter with cold. "At least, it didn't say so in the official handbook. Wild elephants, yes. They b-borrowed some from a traveling fair, apparently. Battering rams, yes - but no one tried four th-thousand warrior jinn. Per-probably couldn't get hold of any."

A series of blows rained down on the hatch, followed by a further shower of ice. A shout of excitement came from Tertius Fume. "Mace men to the front! Smash the hatch!

Smash it! I want to see Marcia Overstrand's expression tomorrow when she wakes to see the Wizard Tower surrounded!" A series of massive blows to the hatch followed. A large chunk of ice landed in front of them, breaking into millions of crystals.

"Let's get out of here," said Septimus. "We can go meet the sled."

"N-no, Sep," said Beetle. "Rule one - once you've C-Called the s-sled, stay where you are. How else is it going to f-find you?"

"I can Call it again."

"It will still go to where you f-first Called it. Then you've just wasted more t-time."

"Well, I'll stop it on its way. We'll see it coming."

"You can't just flag it down like a d-donkey cart."

Another series of blows shook the hatch and dislodged a flurry of ice.

"I...I don't think the sled's going to get here in time, Beetle," said Septimus. "The Castle must be miles away."

"Yeah."

Crash.

"But we have to warn Marcia," said Septimus, "we have to. Hey, Beetle... Beetle, are you okay?"

Beetle nodded, but he was shivering badly.

Another crash came from above, and a huge lump of ice smashed down. Septimus dragged Beetle out of the way and discovered that his fingers didn't seem to be working properly. He waited, huddled with Beetle, for the sound of the ice hatch opening - which must surely come soon. A spray of ice dampened his face and Septimus closed his eyes. Something nudged him. It was the Wizard Tower sled.

The smashing of the Ice Tunnel hatch sent a loud boom along the tunnel, followed by a great crash as the hatch hit the ice below.

"Faster, faster," Septimus urged the Wizard Tower sled, which swish ed through the tunnel, its narrow silver runners cutting through the hoar frost on the ice. It was the most frightening sled ride Septimus had ever taken - and, as someone who had been a passenger of Beetle's, that was saying something. It was not only the speed; they were also traveling in complete darkness. Septimus had Instructed the sled to douse its light. A fine spray of ice flew into the air as they went, and Septimus, with his hands clasping Beetle's waist, was aware that Beetle was getting dangerously cold. He realized he should have sat Beetle behind him to protect him from the icy blast as they traveled, but he did not dare stop now. He told himself that as soon as they reached the nearest hatch in the Castle, he would get Beetle aboveground and into the warmth of the sun. Then he would Transport himself to Marcia - he was pretty good at Transports within the Castle now - and together they would Seal off all tunnels into the Castle. It would be a close-run thing. He figured he needed to be at least two hours ahead of the warrior jinn. But at the breathtaking speed the sled was going, Septimus thought he'd easily manage it. As the sled sped down the long, straight tunnel, Septimus risked a backward glance. He saw a strange sight - a line of tiny pinpricks of light was moving down from the hatch: the silver wings of the warrior jinn were lighting up in the dark. Septimus shivered at the thought of the jinn pouring into the Ice Tunnel, with nothing now but a long, freezing march between them and the Castle. Not that the cold would bother the jinn, or their ghostly leader. The thought of the long journey ahead through the ice began to worry Septimus, and he decided that as soon as the jinn were out of sight he would stop for a moment and swap places with Beetle. He'd try a Heat Spell for himself and hope that it warmed up Beetle a little.

Septimus's plans were interrupted by Tertius Fume's bellow echoing along the tunnel: "To the Castle!" This was followed by the synchronized crunch of marching feet on ice. The warrior jinn were on their way.

To Septimus's consternation, the Wizard Tower sled had chosen that very moment to slow down. It was now crawling along at a snail's pace that Beetle, had he not been shivering uncontrollably, would have derided.

"Faster!" Septimus urged the sled. "Faster!" It did not respond but bumped slowly over a patch of rough ice - the kind that is often found below an ice hatch. Anxiously Septimus looked back to see how fast the warrior jinn were gaining on them. At first he was reassured - they appeared not to have moved at all. He could see a steady flow of tiny silver lights moving down from the Ice Tunnel hatch and then it was hard to tell what was happening. The jinn did not seem to be getting closer and yet the clud-clump sound of their marching feet reverberated through the tunnel. Puzzled, Septimus stared into the dark, and then he realized something rather important - the pinpoints of light were receding. The jinn were marching in the opposite direction. Septimus could not believe what had happened. The sled had gone the wrong way. The Wizard Tower sled came to a halt. At first Septimus thought it had stopped because it had realized its mistake. But then, out of the corner of his eye, he saw the shape of an ice hatch above and remembered what he had told the sled: "Nearest hatch. Fast as you can." Septimus had assumed that the nearest hatch would be in the Castle. In his anxiety about Beetle, he hadn't given any thought to where else the Ice Tunnel might go. In fact, he had assumed that it didn't go anywhere else - after all, where would it go?

He was about to find out. Beetle was dangerously cold, and he had to get him out of the Ice Tunnel fast. Septimus climbed up the icy rungs on the side of the tunnel, UnSealed the hatch and pushed it open. Immediately in front of him was the now familiar black shine of a moving chamber.

Septimus decided to leave the sled free. He pushed Beetle up to the hatch, pulled him through and Sealed it. Then he propelled Beetle into the moving chamber. He placed his hand on the orange arrow and felt the chamber shift.

Where, he wondered, was it taking them?